The variation in the shape of the long-wavelength tail of the intervalence charge-transfer band has been measured in single crystals of the class II SbIII,V mixed-valency compound of Rb2.67SbCl6 from 6 to 310 K. Far-infrared and Raman spectra (50-1000 cm-1) are also reported. The absorption constant is an exponential function of photon energy, i.e. the band edge obeys the Urbach rule. To explain the temperature dependence of the steepness of the exponential band edge it is necessary to include quadratically coupled lattice modes in addition to the linearly coupled intramolecular modes. The mean frequency of this lattice mode is 88(2) cm-1, in the same range as the transverse optic mode (76 cm-1).
|Number of pages||10|
|Journal||Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics|
|Publication status||Published - 1985|
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Physical and Theoretical Chemistry